Sealing is an essential aspect of any cosmetic anodizing process for aluminum alloys—necessary to ensure the corrosion resistance of the surface, and to protect the anodic oxide against uptake of dirt and loss of any incorporated coloring agents. Most sealing processes involve exposing the anodic coating to hot aqueous solutions that cause hydration of the pore structure. Although pure boiling water or steam may be used, additives are often added for efficiency and for improved process control and consistency, allowing lower temperatures to be used.
One way to increase the time efficiently of the pore sealing process is to use solutions such as nickel acetate and chromate solutions. For example, nickel acetate sealing solutions can provide exceptionally good sealing and can also be very time efficient, sometimes providing a good seal in a matter of seconds. However, use of these sealing solutions can have some disadvantages. For example, nickel originating from the nickel acetate sealing solution can leach out from the sealed anodic films, which may not be desirable in certain types of products.